In a pregnant woman with preeclampsia, what are the blood pressure targets and the recommended antihypertensive management, including first‑line agents, dosing, and seizure prophylaxis?

Blood Pressure Management in Preeclampsia

In pregnant women with preeclampsia, severe hypertension (≥160/110 mmHg) requires urgent treatment within 30-60 minutes using IV labetalol, IV hydralazine, or oral nifedipine, targeting BP of 110-140/85 mmHg, with magnesium sulfate administered immediately for seizure prophylaxis in all cases of severe hypertension or neurological symptoms. 1, 2

Blood Pressure Thresholds and Urgency

Severe hypertension is defined as BP ≥160/110 mmHg sustained for ≥15 minutes and constitutes a hypertensive emergency requiring immediate treatment in a monitored setting to prevent maternal stroke and cerebral hemorrhage. 1, 2, 3

Non-severe hypertension (BP ≥140/90 mmHg consistently) should also be treated to reduce progression to severe hypertension and complications such as thrombocytopenia and elevated liver enzymes. 1

First-Line Antihypertensive Agents for Severe Hypertension

Acute Management Options (choose one):

• IV labetalol: 20 mg bolus, then 40 mg after 10 minutes, followed by 80 mg every 10 minutes up to maximum cumulative dose of 220 mg 2, 3

• IV hydralazine: Acceptable alternative to labetalol for acute severe hypertension 1, 3, 4

• Oral immediate-release nifedipine: Acceptable when IV access unavailable or as alternative first-line agent 1, 2

Critical caveat: Short-acting oral nifedipine should be avoided when combined with magnesium sulfate due to risk of uncontrolled hypotension and fetal compromise. 2 Sodium nitroprusside should only be used as last resort in extreme emergencies due to risk of fetal cyanide poisoning. 2

Blood Pressure Targets

Primary target: Systolic BP 110-140 mmHg and diastolic BP 85 mmHg 1, 2, 5

Minimum acceptable target: Systolic BP <160 mmHg and diastolic BP <105 mmHg 2, 3

Rationale: The goal is to decrease mean BP by 15-25% to prevent maternal cerebral hemorrhage while maintaining uteroplacental perfusion. 2

Lower threshold for dose reduction: Reduce or cease antihypertensives if diastolic BP falls <80 mmHg to avoid maternal hypotension and placental hypoperfusion. 1, 5

Maintenance Antihypertensive Therapy for Non-Severe Hypertension

First-line oral agents (for BP ≥140/90 mmHg):

• Methyldopa 1
• Labetalol 1, 6
• Long-acting nifedipine 1
• Oxprenolol 1

Second or third-line agents:

• Hydralazine 1
• Prazosin 1

Magnesium Sulfate for Seizure Prophylaxis

Indications for immediate magnesium sulfate administration:

• All women with preeclampsia AND severe hypertension (≥160/110 mmHg) 1, 2
• All women with preeclampsia AND neurological signs or symptoms (severe headache, visual scotomata, altered mental status) 1, 2
• All women with proteinuria AND severe hypertension 1

Dosing regimen: Loading dose of 4-5 g IV over 5 minutes, followed by maintenance infusion of 1-2 g/hour continuous IV 2, 7

Monitoring for magnesium toxicity:

• Hourly urine output via Foley catheter (target ≥100 mL/4 hours or >35 mL/hour) 2
• Deep tendon reflexes before each dose 2
• Respiratory rate (magnesium can cause respiratory depression) 2

Critical Monitoring Requirements

Maternal monitoring:

• Continuous BP monitoring until hemodynamically stable 2
• Clinical assessment including clonus 1
• Oxygen saturation (maternal early warning if <95%) 2
• Assessment for severe headache, visual changes, epigastric/RUQ pain, shortness of breath 2

Laboratory monitoring (minimum twice weekly, more frequently with clinical deterioration):

• Complete blood count with platelet count 1, 2
• Liver transaminases 1, 2
• Serum creatinine 1, 2
• Uric acid 1, 2

Fetal monitoring:

• Initial ultrasound at diagnosis: fetal biometry, amniotic fluid volume, umbilical artery Doppler 1, 2
• Repeat ultrasound every 2 weeks if initial assessment normal, more frequently if fetal growth restriction present 1, 2

Absolute Indications for Immediate Delivery

Regardless of gestational age, deliver immediately after maternal stabilization if any of the following occur:

• Gestational age ≥37 weeks 1, 2
• Inability to control BP despite ≥3 classes of antihypertensives in appropriate doses 1, 5
• Progressive thrombocytopenia 1, 2
• Progressively abnormal liver or renal function tests 1, 2
• Pulmonary edema 1, 2
• Severe intractable headache, repeated visual scotomata, or convulsions 1, 2
• Non-reassuring fetal status 1, 2

Delivery Timing by Gestational Age

• ≥37 weeks: Deliver after maternal stabilization 1, 2
• 34-37 weeks: Expectant conservative management if maternal and fetal status stable; deliver if any deterioration 1, 2
• <34 weeks: Conservative expectant management at center with Maternal-Fetal Medicine expertise; deliver if maternal or fetal deterioration 1, 2

Common Pitfalls to Avoid

• Do not attempt to classify preeclampsia as "mild versus severe" clinically—all cases may become emergencies rapidly. 1, 2
• Do not use serum uric acid or level of proteinuria as indication for delivery. 1, 2
• Do not routinely use plasma volume expansion in women with preeclampsia. 1, 2
• Avoid ACE inhibitors, ARBs, and direct renin inhibitors—absolutely contraindicated due to severe fetotoxicity. 2
• Avoid diuretics—contraindicated as they further reduce plasma volume. 2

Postpartum Management

• Replace methyldopa with alternative antihypertensive after delivery if it was used during pregnancy. 2
• Continue BP monitoring at least every 4 hours while awake for minimum of 3 days postpartum, as hypertension can worsen between days 3-6 after delivery. 2, 8